This trick is achieved by only rendering rows as they are needed. As they scroll off the top, rows are removed and and new ones are added to bottom of the scrolling element. This is becoming more common as web applications tackle larger amounts of data. I have also seen this technique used for displaying large tables of data in libraries such as SlickGrid, UkiJS, and we use a variant of this at LiquidPlanner for displaying large and complex project schedules.